This invention relates generally to the packaging of semiconductor devices. More particularly, this invention relates to a large semiconductor device package that minimizes the impact of different coefficients of thermal expansion associated with the environment in which the package exists. The invention also relates to processing techniques employed for under-filling of chip dies to thin substrates which require rigid stiffeners to control the flatness of the device packages and reduce bowing affects due to internal stresses caused, for example, by differences in coefficients of thermal expansion between material layers.